Electron gun beam straightener



Oct. 28, 1969 o. SCIAKY 3,475,584

ELECTRON GUN BEAM STRAIGHTENER Filed May 26, 1967 2 Sheets-Sheet 1 u L2 L3 .n'xx xxxx 5 y 7 W/l/AHW/l/l/A 8 Ill! HIGH 9 2 ll 1 suvmx I u 3 I Fg. 2

DAVID SCIAKY INVENTOR.

0. SCIAKY 3,475,584

Filed May 26, 1967 GROUND DAVID SCIAKY I NVENTOR.

United States Patent 3,475,584 ELECTRON GUN BEAM STRAIGHTENER David Sciaky, Chicago, Ill., assignor to Welding Research, Inc., Chicago, 11]., a corporation of Illinois Filed May 26, 1967, Ser. No. 641,678 Int. Cl. 323k 9/00 US. Cl. 219-121 6 Claims ABSTRACT OF THE DISCLOSURE This present disclosure relates to electron beam gun systems and describes a method and apparatus for automatically straightening the electron beam which has been deflected off axis by the magnetic field around the filament so that it is returned to a path essentially parallel to the axis of the gun. Probes which sense the edge of the beam deliver currents to a regulating system which acts upon an electromagnetic beam straightening device.

This invention has reference to electron beam guns and in particular to a method and apparatus for insuring that the electron beam leaves the anode of the electron gun in a direction along the axis or parallel to the axis through the center of the electron beam forming elements in the electron gun.

In an electron gun, as described in Patent No. 3,187,- 216, a directly-heated filament is utilized as a source of electrons. A stream of electrons emanating from the filament is directed 'by suitable electrostatic fields towards a hole in the anode through which the beam passes, the beam being focused by these electrostatic means at some point beyond the aperture or hole in the anode. When the filament is directly heated by a uni-directional current, we find that the steady magnetic field created by the passage of the filament current through the filament loop causes the electron beam to be deflected in a direction at right angles to the electromagnetic field which is transverse to the path of the electron beam. As a result of this bending, the electron beam strikes one side of the hole in the anode and it leaves the anode at some angle with reference to the mechanical axis of the gun. The beam then continues on its path, enters the focus coil at this angle and is focused on the work to be welded. Because the beam enters the focus coil off the axis and away from the center of the focus coil, it is given certain aberrations which are not desirable.

Distortion of the filament due to heating and the re sulting displacement of the filament from the true center of the electron optical system also causes the beam to deviate from the axis.

Due to the misalignment of the beam, the point of impingement of the beam on the work cannot be maintained when the current through the magnetic focus coil is varied. As the current is changed, the spot moves about on the work making it difiicult to adjust the work so that the beam impinges at the desired line of weld.

Indirectly heated filaments have been used in an attempt to correct this difliculty, but their use has added other inconveniences such as the need for additional power supplies for bombarding the emitter, longer heatup time of the emitting surface and additional heat developed in the electron gun due to the additional power supply. Furthermore, the magnetic field in the emitter area is not completely removed, but only reduced in magnitude since. a directly heated filament is needed as a source of electrons to bombard the electron gun emitter.

A directly heated emitter is most desirable since this can be in the form of a filament made from wire or strip material which is easily formed and can easily be replaced when the filament has reached the end of its useful life.

It is the object of this invention to overcome the above ice defects and to provide a beam which moves along a line substantially along the mechanical axis of the electron gun and focus coil assembly.

It is a further object of this invention to provide a gun in which the electron beam passes through the focus coil substantially at its center and parallel to its axis.

It is a further object of this invention to provide a beam straightening device which is automatic in operation.

It is a further object of this invention to provide a beam straightener utilizing a feedback regulator which automatically controls the beam so that it passes through the center of the anode aperture and is directed substantially along the axis of the electron beam gun.

It is a further object of the present invention to provide an electron beam gun apparatus in which the electron beam remains on axis as it passes through the focus coil towards the work although the focus coil current is varied. 1

It is a further object of the invention to provide an electron beam apparatus in which the point at which the electron beam impinges upon the work remains fixed although the focus current is varied.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description in conjunction with the accompanying drawings which are hereafter particularly described and explained:

FIG. 1 is a schematic view showing electrical connections for the various elements of an electron beam gun of the type discussed in this specification.

FIG. 2 is a sectional view of the important elements of the electron gun.

FIG. 3 is a fragmentary sectional view of FIG. 2 rotated FIG. 4 is a diagram of the automatic feedback regulator system for effecting the improvement as claimed in this invention.

In FIG. 1, the various elements of a typical electron gun are shown in fragmentary section along with a schematic view of the electrical connections. One and two are a portion of the clamps which fasten and support the filament 3 in proper relationship to the cathode elec trode 4 and the anode electrode 5. The heating current for the filament 3 supplied by a high current, low voltage DC power supply 6. This power supply is fed from the three-phase power supply lines L1, L2 and L3. The terminals 23 and 7 are connected to electrodes 1 and 2 and thus feed direct current to filament 3 of suflicient intensity to bring the operating temperature of the filament to the emission temperature to insure an adequate supply of electrons. The high voltage power supply furnishes a direct current of the desired voltage for maintaining the required electrical field between the cathode 4 and anode 5. The negative conductor 8 is connected to the conductor 22 and the conductor 9 completes the cir cuit to the cathode electrode 4. The positive conductor 10 from the high voltage supply has connection with the anode 5 and a parallel circuit including conductor 11 is connected to the workpiece 12 and grounded. An electron bearn will be formed which will be directed to and passed through the hole in the anode 5 and focused onto the work 12 at the point where it is desired to produce a weld.

FIG. 2 is an enlarged view of the filament which shows the conditions that exist around the filament when current is passed through it. The current I passing through the filament produces a magnetic field around the filament, the dots and Xs indicate in cross-section the field which surrounds the space above and below the filament.

FIG. 3 is a drawing of the same filament rotated 90 showing the magnetic lines of force surrounding the filament. Although the field strength adjacent to the lower portion of the filament is not more than 8l0 gauss, this flux is of sufficient intensity to cause the electrons being emitted from the filament to deflect the beam oif axis as it is accelerated from velocity as it emerges from the filament to greater than one-third the velocity of light as it approaches the anode. In order to compensate for and cancel the magnetic field under the filament in the path of the electron beam, we provide electromagnets 13 as shown in FIG. 3 on either side of the filament which produce a magnetic field in a direction opposite and equal to the field produced by the current passing through the filament. The field produced by the electromagnets 13 thus straightens the beam and allows it to pass through the anode aperture and on to the work in a path which is substantially along the axis of the electron gun and allows the beam to pass through the center of the focus coil 21. In this way, because the beam passes through the center of the focus coil 21 a minimum of aberrations are produced in the beam and the beam is not displaced when the focus coil current is changed to effect the change in focal length. The electromagnetic coils 13 may be fed from an auxiliary direct current power supply which may be manually controlled, the operator adjusting the current through the coils until he notices that the electron beam trajectory is the desired one along the axis of the gun. It is preferable, however, to provide an automatic control for beam centering and to this effect, the system illustrated in the schematic diagram of FIG. 4 is shown to illustrate one means by which the automatic straightening of the beam may be effected. Directly under the anode and insulated from it by insulator 22 are mounted split ring pick-ups which will collect any of the fringe electrons at the periphery of the beam which strike these ring segments. Should the beam be deflected to the left, these electrons will strike split ring segment 14, pass through resistor 16 across which a voltage E will be developed. Should the beam be deflected in the opposite direction, to the right, split ring segment will pick up the current which will pass through resistor 17 to the ground and develop across resistor 17 voltage E With the electron beam centered between split ring segments 14 and 15, the number of electrons per second reaching 14 will equal those reaching 15 and the voltage across resistors 16 and 17 will be equal and the voltage across terminals 18 and 19 will be zero. Should the beam move toward segment 14, terminal 19 will become negative with respect to terminal 18. Should the beam be deflected toward segment 15, terminal 19 will become positive with respect to terminal 18. These voltage signals between terminals 18 and 19 and the ground are fed to the input terminals of the feedback regulator whose output current feeds the beam straightening coils 13, regulating the current through coils 13 in such a way that it tends to maintain the beams so that it centers itself along the axis of the gun in such a way that equal voltages are developed across resistors 16 and 17. When the beam deflects to the left, the feedback regulator 20 automatically adjusts the current through 13 by increasing it so that the beam is brought toward the center. Should the beam be deflectedtoward the right, the feedback regulator will decrease the current through coils 13 so that the beam returns again to the center. This regulator means thus works in such a fashion that the beam is maintained automatically along a path substantially in line with the axis of the electron gun. This is maintained automatically without the necessity of any manual adjustment.

The apparatus within the feedback regulator 20 may comprise, in one form, a first electromagnetic relay which is energized when terminal 18 is negative with respect to terminal 19 and is deenergized when the voltage between terminal 18 and terminal 19 becomes zero, and a second electromagnetic relay which becomes energized when terminal 19 becomes negative with respect to terminal 18 and is deenergized when this voltage reaches zero.

When the first relay is energized, it energizes a motor which drives a variable transformer feeding a DC. power supply for coil 13 in such a direction so as to vary the current through coil 13 and thus vary the magnetic field of coil 13 so as to progressively deflect the electron beam towards the axis until the beam is centered in the aperture between the segments 14 and 15. When the voltage drop across terminal 18 and terminal 19 reaches zero, the relay is deenergized and the motor-stops. Should the second relay be energized, the motor will be driven in the opposite direction so as to cause the beam to move again towards the axis until the currents reaching 14 and 15 are equal and the beam is again centered automatically.

Fully electronic systems may also be used to accomnlish the same regulating action.

For more complete details of the electron gun, reference can be made to Patent No. 3,187,216 issued in the name of David Sciaky and entitled Electron Gun. It is understood that the invention is not to be limited to or by details of construction of the particular embodiment thereof illustrated by the drawings as various other forms of the device will, of course, be apparent to those skilled in the art without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

1. An electron gun of the type using a directly heated filament about which is generated a magnetic field, electromagnetic means placed substantially along the plane passing through the emitting surface of the filament for generating a magnetic field to counter aforesaid first magnetic field and means for regulating the intensity of said second magnetic field.

2. An electron gun in accordance with claim 1, in which the electron gun includes beam forming electrodes having circular symmetry about an axis along which electrons are directed.

3. An electron gun in accordance with claim 2, including means supported and insulated from one of said beam forming electrodes for sensing the deviation of aforementioned electron beam, and means cooperating with said sensing means for regulating the intensity of the aforesaid second mangetic field, in order to direct the electron beam along a path substantially coincident with the aforementioned axis.

4. An electron gun in accordance with claim 3, in which the said means for sensing the deviation of the beam includes a first current sensing means positioned along the axis of the electron gun and positioned so as to skirt one edge of the, beam, a second current sensing means positioned so as to skirt the diametrically opposite edge of the beam and circuit means for sensing the difference in the intensities of current striking the two current sensing means.

5. An electron gun in accordance with claim 4, including regulating means operable from the said difference in currents, and electromagnetic means operable from said regulating means for producing a magnetic field for deflecting the beam so as to cause the value of the said difference current to reach zero by equalizing the current reaching the two aforementioned current sensing means.

6. An electron gun in accordance with claim 5, in which the aforementioned current sensing means are positioned immediately below the said beam forming electg'odes and held in position by means of insulating memers.

References Cited UNITED STATES PATENTS 2,640,948 6/1953 Burrill. 3,152,238 10/1964 Anderson 2l9-121 JOSEPH V. TRUHE, Primary Examiner W. DEXTER BROOKS, Assistant Examiner 

